1. Field of the Invention
The present invention relates to a pressure detection unit for use in e.g. an information input device that allows information input by a user's pressing on a panel member.
2. Description of Related Art
Conventionally, a pressure-sensitive sensor is known as a device having a press detection function for detecting a pressing force (see Patent Document 1). The pressure-sensitive sensor disclosed in Patent Document 1 comprises plastic films facing and bonded to each other via an insulating layer having adhesion layers on the front and back faces thereof, each plastic film including an electrode and a pressure-sensitive ink layer laid one on the other.
Further, the present applicant filed a patent application for an arrangement configured for restricting reduction in visibility of a displaying portion when the pressure-sensitive sensor of Patent Document 1 is to be used in a touch panel from which visibility is required (Japanese Patent Application No. 2008-330288, WO 2010/074116). The pressure-sensitive sensor for a touch panel disclosed in Japanese Patent Application No. 2008-330288 (WO 2010/074116) has a same arrangement for its vertically stacked portion as the arrangement disclosed in Patent Document 1. In addition, as shown in FIG. 14, a pair of electrodes 21a, 22a are disposed in the form of frames along edges of plastic films 21A, 22A and pressure-sensitive ink 23a, 23b are provided in the form of spots distributed along the edge portions of the plastic films 21A, 22A. Incidentally, in an adhesion layer 30, an insulation member 30A is disposed between two layers of adhesion material 30B so as to avoid formation of electric conduction between the electrode 21a and the electrode 22a. 
In the above, the pressure-sensitive sensor, as shown in FIG. 15, includes a bump 24a as a load transmission member 24 on the outer face of the plastic film 22A. With this arrangement, when a pressing force is applied to the pressure-sensitive sensor along the thickness direction, the portion of the plastic film 22A corresponding to the pressure-sensitive ink 23b is supported from under, so that the applied pressing force can be transmitted in a reliable manner without dispersion thereof as a force to be utilized for deformation of the plastic film 22A.
Patent Document 1: Japanese Unexamined Patent Application Publication 2002-48658